Extra Dose Measurement of Differential Slice Thickness of MVCT Image with Helical Tomotherapy

토모테라피 치료 시 MVCT Image의 Slice Thickness 차이에 따른 선량 비교

  • Lee, Byungkoo (Department of Radiation Oncology, Korea University Anam Hospital) ;
  • Kang, Suman (Department of Radiological Science, Dong-eui University)
  • 이병구 (고려대학교 안암병원 방사선 종양학과) ;
  • 강수만 (동의대학교 방사선학과)
  • Received : 2013.01.10
  • Accepted : 2013.04.19
  • Published : 2013.04.30


Helical Tomotherapy is an innovative means of delivering intensity modulated radiation therapy (IMRT) using a device that merges features of a linear accelerator and helical computed tomography (CT) scanner. Hereat, during helical tomotherapy process, megavoltage computed tomography (MVCT) image are usually used for guiding the precise set-up of patient before/after treatment delivery. But which would certainly increase the total dose for patients, this study was to investigate the imaging dose of MVCT using the cylindrical "Cheese" phantom on a tomotherapy machine. A set of cylindrical "Cheese" phantom was adopted for scanning with respectively pitch value (1, 2, 3 mm) with same number slice (10 slice), same length (approximately 9 cm) and phantom set-ups on the couch of tomotherapy system. The average MVCT imaging dose were measured using A1SL ion chamber inserted in the phantom with preset geometry. The MVCT scanning average dose for the cylindrical "Cheese" phantom was 2.24 cGy, 1.02 cGy, 0.81 cGy during respectively pitch value (pitch 1, 2, 3 mm) with same number slice (10 slice), and same length's average dose was 2.47 cGy, 1.28 cGy, 0.88 cGy respectively (pitch 1, 2, 3 mm). Two major parameters, the assigned pitch numbers and scanning length, where the most important impacts to the dose variation. The MVCT dose was inversely proportional to the CT pitch value. The results may provide a reliable guidance for proper planning design of the scanning region, which is valuable to help minimize the extra dose to patient. Questionnaires were distributed to Radiology departments at hospitals with 300 sickbeds throughout the Pohang region of North Gyeongsang Province concerning awareness and performance levels of infection control. The investigation included measurements of the pollution levels of imaging equipment and assistive apparatuses in order to prepare a plan for the activation of prevention and management of hospital infections. The survey was designed to question respondents in regards to personal data, infection management prevention education, and infection management guidelines.

의료용 선형가속기 (linear accelerator)와 나선형 컴퓨터 단층 촬영 장치 (helical computed tomography scanner)의 결합 장치인 토모테라피는 세기 변조 방사선 치료 (intensity modulated radiation therapy(IMRT))의 큰 혁신을 이끌었다. 토모테라피 치료 과정에서, Megavoltage computed tomography (MVCT) 영상획득은 치료 환자의 정확한 자세 정렬을 위해 치료 전 또는 후에 이용된다. 그러나 이는 환자의 총 선량을 증가시키는 결과를 만들며, 본 연구는 이처럼 MVCT 영상 획득 시 증가되는 선량을 Cylindrical "Cheese" Phantom을 이용하여 측정, 비교하였다. 각각의 pitch 별로 (1, 2, 3 mm) 동일한 개수의 slice (10 slice), 그리고 동일한 length (약 9 cm)를 scanning하여, 이때의 선량 (MVCT Scanning Dose)을 A1SL ion chamber를 이용하여 측정하였다. 측정 결과 동일한 Slice 개수 (각각의 pitch 당 10개)일 때, MVCT scanning dose의 평균값은 각각 (pitch 1, 2, 3mm) 2.24 cGy, 1.02 cGy, 0.81 cGy가 측정되었다. 동일한 length에서 MVCT scanning dose의 평균값은 각각 (pitch 1, 2, 3mm) 2.47 cGy, 1.28 cGy, 0.88 cGy가 측정되었다. 이는 할당된 pitch와 scanning length가 MVCT scanning dose에 큰 영향을 미치는 가장 중요한 매개 변수임을 말하며, pitch는 MVCT scanning dose와 역비례 관계를 나타냈다. 때문에 적절한 pitch와 scanning length의 선택으로 치료 선량 외의 추가 선량을 최소로 줄여야 하겠다.



  1. E. G. A. Aird, "Second cancer risk, concomitant exposure, and IRMER 2000." Br. J. Radol. 77, pp. 983-985, 2004
  2. Mackie T R, Holmes T, Swerdloff S, et al. "Tomotherapy: a new concept for the delivery of dynamic conformal radiotherapy." Med Phys 20, pp. 1709-1719, 1993
  3. Lisa J. Forrest, Thomas Rockwell Mackie, Ken Ruchala, et al. "The utility of megavoltage computed tomography image from a helical tomotherapy system for set-up verification purposes." Int J Radiat Oncol Biol Phys 60, pp. 1639-1644, 2004
  4. Rajesh A. Kinhikar, Zubin Master, Dipak S. Dhote, and Deepak D. Deshpande, "Initial dosimetric experiience with megavoltage computed tomography detectors and estimation of pre and post-repair dosimetric parameters of a first helical Hi-Art II tomotherapy machine in india." Med Phys 34, pp.73-79, 2009
  5. Ruchala KJ, Olivera GH, Schloesser et al. "Megavoltage CT on a tomotherapy system." Phys Med Biol 44, pp. 2597-2621, 1999
  6. Liu B, Bai M, Fei XL, et al. "Optimization of patient dose parameters of CT examination." Zhong Guo Yi Liao Zhuang Bei 23(3), pp. 54-56, 2008
  7. Amish P. Shah, Katja M. Langen, Kenneth J. Ruchala, et al. "Patient dose from megavoltage computed tomography imaging." Int J. Radiation Oncology Biol. Phys, Vol. 70, No. 5, pp. 1579-1587, 2008
  8. Acceptance Test Procedures and Dosimetry Guide. Tomotherapy Inc. 2005
  9. Mackie TR, Balog J, Ruchala K, et al. "Tomotherapy Semin" Radiat Oncol 9, pp. 108-117, 1999
  10. Sanford L. Meeks, Joseph F. Harmon, Katja M. Langen, et al. "Performance characterization of megavoltage computed tomography imaging on helical tomotherapy unit." Med Phys 32, pp. 2673-2681, 2005
  11. Zeidan O A, Langen K M, Meeks S L, et al. "Evaluation of image guidance protocols in the treatment of head and neck cancers." Int J Radiat Oncol Biol Phys 67, pp. 670-677, 2007
  12. Beavis A W, "Is tomotherapy the future of IMRT?" Br J Radio, 77(916), pp. 285-295, 2004

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